This invention relates generally to television motor driven tuner systems and more particularly to those incorporating programmable channel selection.
In a typical television receiver having a remote control system, a viewer actuated transmitter produces a command signal which operates circuitry within the television producing a "channel-up" or "channel-down" initiate command. Responsive circuitry within the receiver activates a motor which drives the channel selector to the next position. In general, system operation allows either channel-by-channel selection or a programmed skip sequence. In the former individual viewer commands are necessary to move the selector between each channel position while in the latter a programming mechanism selects certain channels which are "skipped over" by the channel selector. For example, in a typical reception area having operative broadcast stations assigned to channels 2, 5, 7 and 9, channel-by-channel operation would require three commands to move the selector from channel 2 to the next higher operative channel 5. In contrast a programmed system operation would cause the selector to go directly from channel 2 to 5 in response to a single command. Similarly, once tuned to channel 5 a channel-up command would move the system directly to channel 7 skipping the vacant channel 6 and so on.
Typical systems for programmed channel skipping use mechanical arrangements which in general comprise a bidirectional electric motor operable in a selected direction by the use of individual relays. Initiate means cause the motor to start rotation in the desired direction. A carryover mechanism comprising a cam coupled to the motor and switch maintain the appropriate relay connection once channel selector rotation has been initiated until the next channel is reached at which point the carryover switch opens. In the absence of a skip action the selector stops and another initiate command is required for further movement.
In most mechanical systems, a toggle switch coupled to the motor is set in the appropriate direction by the initial rotation of the motor. Programmed operation of such a system overrides the channel-by-channel carryover using the mechanically toggled switch and a program skip switch. The skip switch is actuated by cams which may be positioned to provide an alternate motor relay connection during the inactive time of the carryover. The system then simply "rides through" the channel and goes on. The function of the toggle switch is to indicate the motor direction to be maintained. While providing satisfactory operation, such systems exhibit difficulties of limited access to the programming mechanism and impose restraints upon the mechanical configurations which may be employed often frustrating aesthetic and viewer convenience aspects of receiver design.
The subsequently developing electronic systems generally utilize a similar bidirectional motor controlled by a pair of triacs which supply power to the appropriate motor windings to effect rotation in the desired direction. The triacs are controlled by electronic latching circuitry responsive to the channel-up or channel-down viewer commands. Programming is achieved by mechanically operative cams associated with the channel selector which may be positioned to interrupt motor rotation at desired channels. Such circuits generally include complex latch release circuitry to accomplish this function rather than simple switching arrangements which characterize the earlier mechanical systems. While performing satisfactorily and providing significant advantages in design flexibility over earlier mechanical systems, such electronic systems are relatively complex and costly.